Adsorption of Basic Chromium Sulfate Used in the Tannery Industries by Calcined Hydrotalcite

Abstract

The sorption behavior of the chemical species of Cr(III) from aqueous solutions by hydrotalcite calcined products was inves- tigated considering the equilibrium pH (5.0 to 8.9) and the chromium concentration in aqueous solution (from 10.6 to 430.0 mmol/L) to obtain the corresponding isotherms. Each solution was prepared from basic Cr(III) sulphate which is a primary tanning agent used in the tannery industries. In this work no previous oxidation treatment was done to form Cr(VI) in order to remove the chromium from aqueous solutions by hydrotalcite. The amount of chromium in the remaining solutions after the sorption processes in a batch system by visible spectroscopy (Vis) was determined. The calcined hydrotalcite before and after the contact with the chromium(III) solutions by X-ray power diffraction (XRD), thermogravimetric analysis (TGA) and Fourier- transformed infrared (FT-IR) spectroscopy, were characterized. The specific area by Brunauer, Emmett and Teller (BET) method of each sample was also evaluated. It was found that under the experimental conditions of this work hydrolyzed species of Cr(III) are precipitated on the surface of the calcined hydrotalcite instead other adsorption mechanism, and the sulfate ions were the responsible to regenerated the crystalline structure of hydrotalcite, therefore the results are dis- cussed in terms of both Cr(III) and sulfate chemical species.